The present invention relates generally to an automotive keyless entry system which allows a user of a vehicle to lock/unlock a vehicle door or doors or to operate vehicle devices without an ignition key, other mechanical key or a relatively complicated, memorized code. More specifically, the invention relates to an energy-conservation feature in an automotive keyless entry system.
Conventionally, automotive door locks, trunk lid locks, glove box lid locks, steering lock devices and so forth have been operated by means of ignition or other mechanical keys. Recently, so-called "Keyless Entry Systems", which do not require keys to operate door locks, trunk locks, vehicle window regulators and so forth, have been developed. In such keyless entry systems, a keyboard is provided on the external surface of the vehicle body to allow entry of a preset code authorizing access to one of more desired vehicle devices. The designated vehicle devices are electrically operated when the entered code matches a preset code.
U.S. Pat. No. 4,205,325, to Haygood et al, discloses a keyless entry system for an automotive vehicle permitting a plurality of operations to be achieved from outside of the vehicle by one who is knowledgeable of preset digital codes. Functions such as unlocking the vehicle doors, opening the trunk lid, opening windows, operating the sun-roof or programming the system with a user-preferred digital access code can all be performed by proper sequential operation of a digital keyboard mounted on the outside of the vehicle.
This and other conventional keyless entry systems require the user to accurately input the preset code through the keyboard. Although such keyless entry systems have been well developed and considered useful for eliminating the need for mechanical keys, a serious problem may occur when the user of the vehicle forgets the preset code. If the user is outside of the vehicle and the vehicle door lock device is holding the door locked, the user cannot unlock the door lock until he remembers the preset code.
It would be convenient to operate the vehicle door locks other vehicle devices without using the mechanical keys and/or the preset codes, by one-touch operation on a keyboard. This can be done by somehow identifying users authorized to operate the door locks and other vehicle devices. After such identification, further keyboard operations would be required only in order to identify the vehicle devices to be operated. Identification may be achieved by way of signals at specific frequencies or encoded with specific digital information. However, in such cases, the detector must always remain on so as to be ready to respond to identification of the user, which needlessly drains power from the vehicle battery.